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Repairing M-Audio Bx5a speaker

Discussion in 'Audio' started by kcroy, Feb 10, 2012.

  1. kcroy

    kcroy

    31
    0
    Jan 29, 2012
    Hello,

    Here is a brief summary of my current project:

    [​IMG]

    I am having difficulty ID'ing IC3..

    [​IMG]

    Any tips on getting a more accurate ID, and making sure I get the matching part I need?

    -kcr
     
  2. davenn

    davenn Moderator

    13,290
    1,756
    Sep 5, 2009
    remember Google is your friend, there lots of links and datasheets for that IC :)

    its a dual opamp specifically for tone control amd other audo applications :)

    cheers
    Dave
     
  3. kcroy

    kcroy

    31
    0
    Jan 29, 2012
    Using Google I was only able to find the datasheet I linked. You mentioned there were several - could you point me to some additional ones? Perhaps I am using the wrong terms.

    Regarding this datasheet:

    I don't see a "D" version of the 4850 IC,The one that might be "D" says it would be marked "I". Does this seem like a safe substitution?

    I don't understand the functioning well enough to determine what alternate IC I could use..

    I also checked out the JRC site, but was unable to find a match in their audio IC's : http://www.hk.njr.com/eng/products/products_81.html

    Thanks

    kcr
     
  4. davenn

    davenn Moderator

    13,290
    1,756
    Sep 5, 2009
    The "D" is just a package style

    cheers
    Dave
     
  5. kcroy

    kcroy

    31
    0
    Jan 29, 2012
    ok great thanks! going to put in an order for a few. Excited to get this speaker going again!
     
  6. tedstruk

    tedstruk

    475
    7
    Jan 7, 2012
    powher sirkut is die ing

    Only one way to fix it.
    You must replace both the power caps, and the voltage option switch.
    but look at the image.. the board is fused, change the fuses, and don't tell anyone I told you.;)
     

    Attached Files:

  7. kcroy

    kcroy

    31
    0
    Jan 29, 2012
    The fuses looked fine to me - are they obviously blown, or is that just a good precaution?

    I will go ahead and change both Caps.

    Why do you feel the voltage switch needs replacement?

    Thanks so much!
     
    Last edited: Feb 13, 2012
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,191
    2,693
    Jan 21, 2010
    Measure the fuses with your multimeter to see if they are fused (in some really weird cases the wire can break where you can't see it, but it's rare).

    Unless you switched the 110/230V switch with power applied, it's unlikely anything is wrong with the switch. Even if you did, I would still consider damage to the switch as an unlikely option.

    I agree that at least one of those caps looks worse for wear and on that basis I'd probably replace both out of an abundance of caution.
     
  9. w3am

    w3am

    2
    0
    Jul 20, 2012
    There is a manufacturing flaw in the BX-5A speakers that will guarantee this "blown filter cap" problem (and others flowing from it) will recur on every single one of them unless addressed.

    The root of the problem is the 25VDC voltage rating on the primary 6800uF filter caps.
    Those caps when good measure 23VDC across them, (on my pair anyway). This is inadequate voltage headroom and is a time bomb.
    They need to be up-sized to at least 35VDC to cover the peak voltages coming off the rectifiers.
    I strongly suggest 50VDC caps, to be safe.

    Mine are working fine again now. Good luck.

    g
     
  10. kcroy

    kcroy

    31
    0
    Jan 29, 2012
    Thanks for this. I purchased some 25v caps - This project is still sitting on my shelf, so I'll order some 35v for the extra headroom.
     
  11. w3am

    w3am

    2
    0
    Jul 20, 2012
    The combination of the tight voltage rating and the warm/hot enclosed space inside the cabinets put stress on the components. The electrolytics are the most vulnerable over time to drying out and derating.

    They should be sized to handle in excess of the peak rectifier voltages, which can be estimated by measuring the DC voltage across the caps and multiplying by 1.414. This gives 32.5V in the case of my speakers, which should be typical.
    I elected to upsize their voltage and temp ratings further just to have more margin.

    BTW, the opamps you mention earlier are garden variety 4560 duals. They can be easily found if you have a blown one, or replace with a slightly better 4556.

    Good luck.

    g
     
  12. kcroy

    kcroy

    31
    0
    Jan 29, 2012
    Oh cool, thanks man!
     
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